The present invention relates generally to an injection molding apparatus and, in particular, to a gate assembly for reducing drooling of melt from a sprue bar.
Stack molding provides an advantage over single molding in that it enables the output of an injection molding machine to be at least doubled without significantly increasing its size. Stack mold configurations generally employ a stationary first platen, a movable center platen and a movable second platen. The mold cavities are conventionally located on opposing faces of the movable center platen. The movable center platen and the second movable platen reciprocate to open and close the mold cavities during a production cycle. In a stack molding apparatus, the melt runner system or the manifold system extends through the center platen in order to reach the mold cavities located on each side of the center platen via an equal path length.
Typically, multi-cavity stack molds use a single and movable sprue bar to provide a direct melt channel between the extruder nozzle of the injection molding machine and its hot runner distributor, or manifold, which is mounted in the center section of the stack mold. The manifold delivers melt from the sprue bar into injection nozzles that are associated with each individual mold cavity.
As a result of the reciprocating action of the movable platens, the sprue bar is continuously coupled to and decoupled from the melt source. It is therefore necessary to control the flow of the pressurized melt stream when the sprue bar is decoupled from the melt source so that substantially no drooling occurs.
A valve gated stack injection molding apparatus, such as disclosed in U.S. Pat. No. 5,460,510, controls the flow of melt between platens using valve pin members located in the melt channel. The upstream and downstream nozzles each have valve pins that reciprocate between retracted open positions and closed positions in which the valve pins are seated in respective gates. This valve pin arrangement has several disadvantages. The volume of melt that can be transferred through the nozzles is decreased and the pressure in the nozzles is increased because the valve pins are located and move inside the melt channel. Further, the melt experiences additional shear stress as it travels around the valve pins and through the nozzles, which causes flow lines in a molded part.
A thermal gated melt transfer system, such as disclosed in U.S. Pat. No. 4,891,001, controls the flow of melt between platens using a combination of heated nozzles. A disadvantage of thermal gated melt transfer systems is that the flow of pressurized melt is impeded by the relatively small diameter gate defined in each heated nozzle. Stack molds require the transfer of a large amount of melt, which warrants a larger diameter nozzle gate. If the nozzle gate diameter is increased, the melt stream cannot effectively be frozen and therefore, drooling and stringing of molten material occurs. Furthermore, there is a delay associated with cooling and remelting of the melt in the nozzle gate for each molding cycle.
Other stack injection molding devices are disclosed in U.S. Pat. Nos. 4,212,626, 4,244,909, 4,586,887, 5,011,646, 5,030,406, 5,044,927, 5,069,615, 5,458,843, 5,910,327, and 5,968,562. U.S. Pat. No. 5,044,927 discloses a disengageable link between a movable machine nozzle and a sprue bar. The ""927 patent does not include an anti-drooling mechanism.
An improved stack mold melt transfer system is particularly needed for large scale molding operations involving large volumes of melt being transferred at one time. In such cases, it is desirable to have larger diameter melt passages that are not impeded by central valve pins or other obstructions that interfere with the flow of melt within the passages. It is also desirable in such large scale molding operations that drool be controlled in a manner that does not solely rely upon thermal gating as it has been found difficult to achieve a sufficient cooling of the melt over large gate diameters.
It is therefore an object of the present invention to provide a gate assembly for use in a melt transfer system that obviates or mitigates at least one of the above disadvantages.
According to one aspect of the present invention there is provided an injection molding apparatus comprising: a first sprue bar element having a first sprue channel for receiving a melt stream of moldable material under pressure; a second sprue bar element having a second sprue channel for selectively receiving the melt stream from the first sprue channel; a manifold having a manifold channel for receiving the melt stream from the second sprue channel and delivering the melt stream to a nozzle channel of a nozzle; a mold cavity receiving the melt stream from the nozzle, the nozzle channel communicating with the mold cavity through a mold gate; a first gate assembly coupled to an outlet of the first sprue bar element for selectively restricting the flow of the melt stream from the first sprue channel; a second gate assembly coupled to an inlet of the second sprue bar element for selectively restricting the flow of the melt stream from the second sprue channel; and wherein the first gate assembly and the second gate assembly are movable to restrict the flow of melt from the first sprue channel and the second sprue channel when the flow of the melt stream between the first sprue channel and the second sprue channel is interrupted.
According to another aspect of the present invention there is provided a sprue bar gate assembly for a stack mold, the gate assembly comprising: a first gate assembly coupled to an outlet of a first sprue bar element, a second gate assembly coupled to an inlet of a second sprue bar element and wherein the inlet of the second sprue bar element receives a melt stream of moldable material from the outlet of the first sprue bar element when the first gate assembly and the second gate assembly are in an open position and the inlet and the outlet are aligned.
According to another aspect of the present invention there is provided a stack injection molding apparatus comprising: a stationary platen, a first movable platen coupled to the stationary platen and movable into and out of engagement with the stationary platen, a second movable platen coupled to the stationary platen and movable into and out of engagement with the first movable platen, a first sprue bar element having a first sprue channel for receiving a melt stream of moldable material under pressure, the first sprue bar for coupling to a machine nozzle, a second sprue bar element having a second sprue channel for selectively receiving the melt stream from the first sprue channel, a manifold coupled to the first movable platen, the manifold having a manifold channel for receiving the melt stream from the second sprue channel and delivering the melt stream to a first nozzle channel of a first nozzle and to a second nozzle channel of a second nozzle, a first mold cavity provided between the stationary platen and the first movable platen, the first mold cavity receiving the melt stream from the first nozzle channel through a first mold gate, a second mold cavity provided between the first movable platen and the second movable platen, the second mold cavity receiving the melt stream from the second nozzle channel through a second mold gate, a first gate assembly coupled to an outlet of the first sprue bar element for selectively restricting the flow of the melt from the outlet and wherein the first gate assembly is movable when the flow of the melt stream between the first sprue channel and the second sprue channel is interrupted.
According to still another aspect of the present invention there is provided an injection molding apparatus comprising: a sprue bar having a channel extending therethrough, the channel having an inlet for receiving a melt stream of moldable material; a manifold having a manifold channel for receiving the melt stream from an outlet of the sprue channel and delivering the melt stream to a nozzle channel of a nozzle; a mold cavity receiving the melt stream from the nozzle, the nozzle channel communicating with the mold cavity through a mold gate; a melt transfer device located along the length of the sprue bar, the melt transfer device for selectively providing a path for the melt stream to flow between a first portion of the sprue bar and a second portion of the sprue bar, the melt transfer device being movable to interrupt the path; and a gate assembly coupled to the melt transfer device, the gate assembly being movable to restrict the flow of melt from at least a first channel of the first sprue bar portion of the sprue bar when the path is interrupted.
According to another aspect of the present invention there is provided an injection molding apparatus comprising: a first sprue bar element having a first sprue channel for receiving a melt stream of moldable material under pressure; a second movable sprue bar element having a second sprue channel for selectively receiving the melt stream from the first sprue channel, the second sprue element having a first position and a second position relative to the first sprue bar element; a first gate assembly located outside the first sprue channel and coupled to an outlet of the first sprue channel; a second gate assembly located outside the second sprue channel and coupled to an inlet of the second sprue channel; and wherein the first gate assembly and the second gate assembly are movable to restrict the flow of melt from the first sprue channel and the second sprue channel when the second sprue bar element moves from the first position to the second position.
According to another aspect of the present invention there is provided an injection molding apparatus comprising: a first sprue bar element having a first sprue channel for receiving a melt stream of moldable material under pressure; a second movable sprue bar element having a second sprue channel for selectively receiving the melt stream from the first sprue channel; a first gate assembly located outside the first sprue channel and coupled to an outlet of the first sprue channel, the first gate assembly being movable from a first position to a second position; a second gate assembly located outside the second sprue channel and coupled to an inlet of the second sprue channel, the second gate assembly being movable from a first position to a second position; and wherein the first gate assembly and the second gate assembly cooperate to control the flow of melt from the first sprue channel and the second sprue channel.
According to still another aspect of the present invention there is provided an injection molding apparatus comprising: a first sprue bar element having a first sprue channel for receiving a melt stream of moldable material under pressure; a second movable sprue bar element having a second sprue channel for selectively receiving the melt stream from the first sprue channel, the second movable sprue bar element being movable between a melt delivery position and a melt interrupted position; a first gate assembly located outside the first sprue channel and coupled to an outlet of the first sprue channel, the first gate assembly being movable from a first position to a second position; a second gate assembly located outside the second sprue channel and coupled to an inlet of the second sprue channel, the second gate assembly being movable from a first position to a second position; and wherein the first gate assembly and the second gate assembly are actuated by the movement of the second movable sprue bar element from the melt delivery position to the melt interrupted position.
The present invention provides advantages in that drool is reduced inside a stack injection molding machine without disrupting the flow of melt inside the channel.